Disregarding any other difference between lenses, I would personally pay an extra $180 for the 35mm lens. Why? A 35mm lens is a magic angle to me -- it's how I see.
When I started with DSLRs and a crop-sensor body I figured I could use my 28-105mm lens on the camera; it's focal length would be 42-152mm, or thereabouts. I also had a 20mm lens, so that would become 30mm on the new DSLR, and I thought that those two would work well for me. The trouble is, the zoom was always too long. The prime was always too short. Arguably, it was not a big deal because I just had to take a few steps forward or backward most of the time, however I found myself needing to do this all the time. It drove me nuts! I eventually got a 24mm prime lenses, which gave me 36mm on the crop-sensor DSLR, and all was right with the world again. Now, on a full frame DSLR, I use a 35mm lens, and that's great, too.
For me, the difference between 35mm and 40mm is significant in how much I can enjoy photography. It's well worth the cost difference to me.
Also, I wouldn't be at all surprised if there are some performance differences to those lenses that make the 35 command a higher price, as detailed in the Flickr discussion you linked to.